1. Field of the Invention
This invention pertains generally to video compression encoding, and more particularly to inter and intra coding using directional discrete wavelet transforms (DDWT).
2. Description of Related Art
Advanced video coding can utilize both spatial and temporal predictions to increase coding gain. Intra compression coding utilizes spatial prediction, exploiting spatial redundancy, in which each sample in an n×n block is predicted from the neighboring constructed reference samples. The resulting picture is referred to as an I-picture. Traditionally, I-pictures are encoded by directly applying the transform to all macroblocks in the picture, which generates a larger number of data bits compared to that of inter coding performed between the frames of a video sequence. In creating an I-picture, a “difference” or residual image is generated in response to subtracting the intra frame predicted image from the original input image. In many systems a Discrete Cosine Transform (DCT) transform is applied to this residual image with the resulting coefficients being adaptively quantized and coded into a bit stream. Increased compression is provided as the amount of data required for the residual image is reduced when using an accurate intra prediction. Intra frame prediction differs from inter frame prediction as it is utilized within a single frame.
Inter compression coding has many similarities with the above, however, it utilizes temporal prediction exploiting temporal redundancy, in which each sample in an n×n block is predicted from pixels in neighboring pictures/frames. The resulting picture is referred to as a P-picture (predicted), or B-picture (Backward-prediction) depending on the prediction direction.
The use of mode-dependent directional transforms (MDDT) provide some improvement over Advanced Video Coding (AVC) for intra coding, but these benefits are significantly reduced in response to application on a full Group Of Pictures (GOP). For example, the use of MDDT on class C (e.g., 832×480 pixels) and class D (e.g., 416×240 pixels) sequences results in less than 2% average bitrate reduction as measured by the average percentage Bjontegaard (BD) rate changes as specified in ITU-T SG16/Q6 Doc. VCEG-A111, while in 1-frames the improvement is only (7-8%) average BD-Rate reduction. MDDT is not used for inter prediction errors, which also contain direction information, because the inclusion of explicit detection and transmission of edge direction information would introduce significant overhead and reduce overall performance. In addition, MDDT is complex (e.g., hardware and/or software) and does not provide high visual quality.
Current techniques of intra and inter coding adversely impact visual quality of reconstructed images, in particular near feature edges.
Accordingly, a need exists for a system and method of performing inter and intra coding with improved accuracy and reduced feature distortion. These needs and others are met within the present invention, which overcomes the deficiencies of previously developed transform coding systems and methods.